Conventionally, for example, a control device for a multi-phase rotary machine shown in the Patent Literature 1 described below and an electric power steering device using the control device are known. According to the conventional control device for the multi-phase rotary machine, when any of a group of a plurality of MOSs forming a first inverter part and a group of a plurality of MOSs forming a second inverter part is fixed at the ON state and thus, a short occurs in a system of one of the first and second inverter parts, a control part is configured to control all of the MOSs of the malfunctioning system to the OFF state to stop driving the motor by the malfunctioning system. Further, the control part is configured to control the MOSs of the normal system so as to cancel the brake torque generated in the malfunctioning system or reduce the influence on the driving of the motor.